1. Field of the Invention
This invention relates to a jib hold rod securing device to reposition or change the position of the base end of a jib hold rod (or a desired suspension rod) holding a jib when in its stretched out position between the top portion of a boom and the base end of the jib in a manner to match the jib in its stretched-out and take-in positions.
2. Description of the Related Art
In FIGS. 7 and 8, numerals 1, 2 and 3 represent an upper rotary body of a crane, a boom liftably mounted to the upper rotary body and a jib (a pneumatic jib), respectively.
When not in use, the jib 3 is taken in and held under the lower surface of the boom in a desired manner as shown in FIG. 7 with imaginary lines and, for its lift-up operation, stretched out to the position of the top portion of the boom as described hereinbelow.
(I) Jib feet 3a provided on the two sides of the end portion of the jib are engaged and linked with point pins 4 provided on the two sides of a boom head 2a and, with an auxiliary hook 5 engaged to the top portion of the jib, an auxiliary rope 6 is taken up while the boom 2 is lifted up. Thus, the jib 3 is swung forward with the engagement linkage as its fulcrum, as shown in FIG. 7 with imaginary lines.
(II) After the boom is turned back down almost horizontally and, with the jib 3 left supported by the auxiliary hook 5 and the auxiliary take-up rope 6, a pair of right and left jib hold rods 7 and 7 are laid so as to bridge between the boom head 2a and the top portion of the jib to support the jib 3 in its stretched-out position as shown in FIGS. 7 and 8 with solid lines; the auxiliary rope 6 is then loosened.
As shown in FIGS. 7 and 8 with chain lines, the jib hold rods 7 are initially fixed to the jib 3 with their top portions and base portions pinned down to the top portion and base portion of the jib, respectively.
When the jib is stretched out, both of the rods 7 have their base portions released from the base portion of the jib and shifted upward so that their top portions are fixed to the top portion of the jib serving as their fulcrum, to have their base portions fixed to the summit portion of the boom head 2a as shown in FIGS. 7 and 8 with solid lines.
According to the conventional technology, however, it was not possible to adjust the position of a jib in a manner to match its stretched-out and taken-in state, allowing:
a. The base portion of a rod to be released from either of the base portion of the jib and the boom head 2a; and PA1 b. The heavy rod 7 weighing roughly 20 kgs to be lifted up and down and its base portion to be pinned down.
All the above-described operations have conventionally needed to be carried out only when the jib is in its stretched-out position as shown in the two drawings with solid lines. Thus, the conventional technology inevitably requiring high-elevation work standing on a stepladder as shown in FIG. 7 or on the jib 3, forces stress on workers engaged in such a jib repositioning and exposes them to a danger and risk.
Against the above-described background, the present invention has as its purpose to provide a jib hold rod securing device for cranes such as a jib repositioning with less danger and risk as well as labor.
The above, and other objects, are achieved according to the present invention by a crane having a boom and a jib swingable on the boom between a taken in position and a stretched out position. A jib holding construction includes a jib hold rod movably mounted on the jib between a first position in which the base end of the jib hold rod is connected to the jib when the jib is in the taken in position, and a second position in which the base end of the jib hold rod is connected to a portion of the boom for supporting the jib in the stretched out position. The rod holding means are mounted to the jib and are independent of the boom for selectively moving the base end of the jib hold rod at a correct position for connection to the boom when the jib is swung to the stretched out position.
According to an embodiment of the invention, the rod holding means comprises a link selectively connected between the base end of the jib hold rod and the jib.
According to another embodiment of the invention, the rod holding means comprises a link selectively connected between the base end of the jib hold rod and the jib.
According to another embodiment of the invention, the jib hold means comprises a bracket on the base end of the jib hold rod, the bracket having an elongate slot. A link has one end swingably mounted to the jib and another end slidably mounted in the slot. Means are provided for selectively holding the another end of the link in a portion of the slot such that the base end of the jib hold rod is at the correct position for connection to the boom.
According to another embodiment of the invention, the link is articulated at a mid-portion, whereby the link can bend about the articulation to move the jib hold rod between the first and second positions. Means are also provided for holding the link such that the jib hold rod is in the second position, the holding means comprising a gas spring mounted between the jib and the link.
According to yet a further embodiment, the rod holding means comprises a variable length link connected between the jib and the base end of the jib hold rod, the variable length link comprising a gas spring.
A jib hold rod securing device for cranes according to an aspect of the present invention makes it possible to preset the jib hold rod in its jib holding position with the use of the rod holding means at a stage of jib stretching-out operation where the jib is still operable from the ground before stretched out and thus allows laborious rod shifting work associated with a danger and risk to be carried out easily and safely from the ground.
A jib hold rod securing device for cranes according to another aspect of the present invention is made simple in structure with the rod holding means composed of a link and pins which, in turn, makes it low in cost and simple in handling.
A jib hold rod attaching device for cranes according to yet another aspect of the present invention is structured with the rink kept suspended between the jib and the jib holding rod which makes its handling far more easier.
A jib hold rod securing device for cranes according to another different aspect of the present invention is structured with gas springs employed as a means to hold the link in its stretched position which, under the influence of the gas springs, stretches and holds the link in its stretched position (to set the jib hold rod in its jib holding position), requiring far less labor.
A jib hold rod securing device for cranes according to yet another different aspect of the present invention employs gas springs which themselves serve as the rod holding means, requiring a far simpler structure.